洛谷 - P1142 - 轰炸 - 计算几何

#include<bits/stdc++.h>
using namespace std;
#define ll long long

int n;
ll x[705],y[705];

map<pair<ll,ll> ,ll>m;

void reduction(ll &y,ll &x){
    //if(x==0)
        //y=1;
    //if(y==0)
        //x=1;
    ll g=__gcd(y,x);
    y/=g;
    x/=g;
    /*if(x<0){
        y=-y;
        x=-x;
    }*/
    //cout<<g<<endl;
}

int main(){
    scanf("%d",&n);
    for(int i=0;i<n;i++){
        scanf("%lld%lld",&x[i],&y[i]);
    }

    ll maxnum=0;
    for(int i=0;i<n;i++){
        m.clear();
        for(int j=0;j<n;j++){
            if(j==i)
                continue;
            else{
                ll dy=y[j]-y[i];
                ll dx=x[j]-x[i];
                reduction(dy,dx);
                m[{dy,dx}]++;
            }
        }

        ll tmax=0;
        for(auto i:m){
            tmax=max(tmax,i.second);
        }
        maxnum=max(maxnum,tmax+1);
    }
    printf("%lld\n",maxnum);
    //cout<<__gcd(0,2)<<endl;
    //cout<<__gcd(1,0)<<endl;
}